Thermionic amplifier and circuit arrangement therefor



Jan. 19, 1932. ROUND 1,841,383

'IHERMIONIC AMPLIFIER AND CIRCUIT ARRANGEMENT THEREFOR Filed Feb. 18. 1928 INVENTOR HENRY JOSEPH ROUND AM I TORNEY Patented Jan. 19, 1932 UNITED jsTAT E-s ATEN HENRY JOSEPH -BOU1\TD,-OF LoNnomnnGL'Ann, Assmnon TO RAmo oonrorm'rlorf p or AMERICA, A CORPORATION OEIDELAWARE r 'rnERMIoNIo, AMrLIrI'En Ann-omen: ARRANGEMENT mi-manron-f Application filed February isrwaaseria No. 255,213, and in Great Britain away 23, 1927. a

This invention relates to thermioniciamphfiersfand circult arrangements therefor,

and more particularly to thermionic audio frequency amplifiers of the so-called' resist 5 ance coupled type, i. eLf amplifiersiin which the varying voltage drop occurring across a resistance or resistlve impedance (hereinafter termed the anode resistance) in the 311-2 ode circuit of one valve is transferred to the input side of the next. A

' In one wellknown'form (generally'termed resistance capacity coupling) of resistance coupled amplifier, the anode'of the first valve is connected to the anode battery through ananode'resista'nce and to the gridof'the next valve through a coupling condenser. The grid of the said secondvalveis connected to the cathode through another resistance (generally known as a grid leak) a grid bias battery being interposed, if desired.

In cases in which the first valveis em- .ployed as a detector or rectifier, itfis usual to shunt the anode resistance'bya'condenser which acts as a high "frequencyby-pass. V

In resistance coupled amplifiers, particularly those used in broadcasting;receivers,

' .the use of high magnification'valves and anode resistances of, high value resultsin a 3'0 oif over the higher frequencies, particularly those above 2,000cycles per second, duevery largely to the capacities of the Valvesthem .selves. 7

Moreover, when a by-pass'condenser is'emover the higher frequencies The principal object of the'prese tinvention is to eliminate or minimize to adesired degree the effects set forth hereinbeforep; I .According to this invention an inductive reactance is inserted in the lead from the out- I put electrode of one valve to the input "elec-;

trode of the next. v y Y I The inductive reactance should be of acornparatively large value andmay be suitably formed as an iron-cored choke and, "in the case of a resistance capa'c ity coupled amplifier, may be inserted between the "coupling strong tendency for "the amplification to'f'all condenser and the anode end of the/anode resistance ofthe first valveorbetween the couplinglcondenser and the grid end of the grids leak or between the grid end? ofthe s fgrid leak and the grid of the nextvalvel some' cases it may be found desirable to pro vide such inductive 'reactances connected fill more than one of these positions, though generally one choke only will be found suflicient. 1 The inductive reactan'ce isprefe'rably son constructed and arranged that its insertionoo results in the addition of onlya small amount of capacity between the anode end of the anode resistance of the first valve andflthe grid of the next valve." 1 Y i If desired,'a condenser may be inserted be fl tween the grid ofthje succeeding valve and the cathode thereof,"and further,.thegrid leak may be employed as a damping'resistance' or an'additional resistance maybe in serted between the grid and the cathode; It will be seen that the'additionof the in ductive reactance in combination withthe valve grid capacity and any additional con- 7 denser forms a resonant circuit giving an increase -of"voltage across the'grid and oath ode, thereby tending to neutralize any previous dropof amplificatione The grid leak or an additional resistancejmay be'used to adjust the amount of this resonance; a coniparatively sharp cut-off follows the resonant point, whichcut-oif can, for exa'mple','be adjusted to 5000 or 6000 cycles per second, thereby-cutting out undesirable high note sounds.

Theinductive r'eactance has theadditional.

advantage that its'erves as a block to prevent I high frequency currents passing, into the audio frequency amplifier, and. "thereby minimizes undesirable reaction effects, and p the impositlon of dampingupon-anyktuned circuit which may be associated withthednput circuit of the valve in whose anode cir-v cuit the said reactance is connected. v p

. The invention is illustrated" in the accom-' panying diagrammatic drawings, which show in conventional circuit representation, three f modifications of the said invention.

Referring toFigure 1, 1 is a thermionic valve" comprising-a cathode 2, grid 3, and

anode 4, the last mentioned electrode being,

connected through an anode resistance 5-and the grid of the succeeding thermionic valve,

ing resistance 14 to the grid 9. 15 is a condenser shunting the resistance 5 and battery 6. V r

In the modifications shown in Figures 2 and 3, like parts areindicated by like reference numerals.

of the damping resistance 14 in Fig. 2, and the different location of the choke 8 in Fig. 3.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, what I claim is:

1. In an impedance coupled thermionic amplifier, adapted to operate over a prede-.

termined frequency range and normally producing greater amplification at one end of the range than the other end, the combination with an inductive reactance connected between the anode of one thermionic valve and of a condenser directly connected between the grid of the succeeding valve and the cathode thereof, said condenser being independent'of the said succeeding valve, said condenser and reactance being designed to provide a network resonant to a frequency at said otherend to neutralize drop of amplification at the latter end.

2. In a resistance coupled thermionic aniplifier, adapted to operate over a predetermined frequency range and normally producing greater amplification at one end of the range than the otherend, the combination with an inductive reactance connected between the anode of one thermionic valve and the grid of the succeeding thermionic valve, of a condenser directly connected between the grid of the succeeding valve and the cathode thereof, said condenser being independent of the said succeeding valve, said condenser and reactance being desi gned to provide a network resonant to a frequency at said other end to neutralize drop of amplification at the latter end, and a damping resistance shunting said condenser.

3. An amplifier comprising a plurality of resistively coupled thermionic valves, an inductive reactance between the anode of a valve and the grid of a succeeding valve, and a capacitive reactance connected between the grid and cathode ofsaid succeeding valve, said latter reactance combining with the inductive reactance to form a resonant circuit across the input terminals of said succeeding valve to produce an increase of voltage The said modifications difier from that shown in Figure 1 by the omission across the grid and cathode of said succeeding valve at high frequencies, whereby a decrease in amplification at high frequencies is eliminated.

4:. An amplifier comprising a plurality of resistively coupled thermionic valves, an inductive reactance comprisinga choke coil between the anode of a valve and a grid of a succeeding valve, and a capacitive reac tance connected directly'between the grid and cathode of the succeeding valve, said capacitive reactance together with the grid cathode capacity of the succeeding valve combining with the choke coil inductance to form a resonant circuit across the input terminals of said succeeding valve, and a damping resistance associated with said capacitive reactance to vary the amount of resonance in said resonant circuit.

5. In an amplifier, the combination with a plurality of resistance-coupled thermionic vacuum tubes having a resistance in the anode circuit of the first tube, a grid leak resistance in the input circuit to the second tube, and a coupling condenser in thesaid anode circuit, of an inductivereactance connected in series with said coupling condenser, and a second condenser directly connected in shunt to the input circuit of the second tube, said condenser being so related to said inductive reac tance'as to form an input resonant circuit whereby a decrease-in amplification at relatively high frequencies is compensated for. f

6. The combination in an amplifying system of resistance-coupled vacuum tube amplifiers-in which the amplification at the relatively high frequencies tends to, fall 0E, said amplifiers having a'resistancein the anode circuit of the first tube, a grid leak resistance in the input circuit to thesecond tube, and a coupling condenser in the said anode circuit, an inductive reactance connected in series with said coupling condenser and a second condenser directly connected in shunt to the input circuit'of the second tube, said second named condenser together with the grid-cathode capacity of the secondtube combining with said inductive reactance to form an input resonant circuit-whereby the decrease in amplification at the relatively high frequencies'is compensated for.

7 In an impedance coupledthermionic V amplifier, adapted to operate over a predetermined frequency range and normally producinggreater amplification at one end of therange than the other end, the combination with an inductive reactance connected between the anode of one thermionic valve and the grid of the succeeding thermionic valve, of a condenser directly connected between the grid of the succeeding valve and the cathode thereof, said condenser being independent of the saidsucceeding valve, Said condenser and reactance being designed to provide a network resonant to a frequency at said otherend to neutralize drop of amplification' at the latter end and a high frequeney by-pass condenser connected between range than the other end, the combination.

with an inductive reactance connected between the anode of one thermlonic valve and the gridof the succeeding thermionic valve,

of a condenser directly connected between the grid of the succeeding valve and the cathodethereof, saidcondenser being independent of the said succeeding valve, said condenser and reactance being designed to provide a network resonant to a frequency at said other end to neutralize drop ofamplification at the latter end, said inductive reactance comprisingan iron-cored choke. V

9. In an impedance coupled thermionic am; plifier, adapted to operate over a predetermined frequency range and normally-producing greater amplific'ation'at one end of the range than the other end, the combination with an inductive reactance connected between the anodeof one thermionic valve and the grid of the succeeding thermionic valve,

of a condenser directly connected between the grid of the succeeding valve and the cathode thereof, said condenser being independent of the said succeeding valve, said condenser and reactance being designed to provide a'network resonant to a frequency at saidother'. end to neutralize drop of amplification at the latter end, a path between the anode and cathode of the first valve including a source of current and a resistor, and a path between the grid and cathode ofthe succeeding valve i pendent of the sald succeeding valve, said including a bias source and a resistor.

10. In an impedance coupled thermionic amplifier, adapted to operate over a predee termlned frequency range and normally producing greater amplification at one end of T q associated with th'econdenser to adjust the the range than theeother end, the combination with an inductive reactance connected between the anode and one thermionic valve and the grid of the succeeding thermionic valve, of a con'denserdirectly connected beprovide a network resonant to a frequency, at

said other end to neutralize drop of ampliyficationat the latter end, the connection between the reactanceand the grid of the suc ceeding ,va-lve' including a condenser.

12;- In an impedance coupled thermionic amplifier, adapted to operate over a prede-I termined frequency range and normally pros ducinggreater amplification at the low frequency'end of the range than the high he l V quency end, the combination with an inductive reactance connected between the anode of one thermionic valve and the grid of the succeeding thermionic valve, of a condenser directly connected between the grid of the I succeeding valve and the cathode thereof, said condenser beingindependent of the said succeeding valve, said condenser and reactance I being designed to provide a network resonant to a frequency at said high frequencyend to".

end; 13; In an impedance coupled thermionic neutralize drop of amplification at the latter i amplifier, adapted to operate over a predetermined frequency range and normally producing greateramplification atone endof the range than theother end, the combination wlth an inductive reactance connected between the'anode of one thermionic valve and the grid of the succeeding thermionic valve,

of a condenser directly connected between the grid of the succeeding valve and the cathode thereof, said condenser being inde-.

condenser and reactance being designed to provide anetwork resonant to afrequency at said other end to neutralize drop ofamplification at the "latter end, and an impedance,

network resonance.

HENRY. JOSEPH ROUND. 7

tween the grid of the succeeding valve and the cathodethereof, said condenser being in-:'

dependent of the said succeeding valve, said condenser and reactance being designed to provide a network resonant to a frequency at said other end to neutralize drop of amplification at the latter end, and a condenser connected in series between the reactance" and the anode of the first valve.

11. In an impedance coupled thermionic I firs amplifier, adapted to operate over a prede- 7 termlned frequency range and normally producing greater amplification at one end of the range than the other end, the combina- 

